1. Field of the Invention
The present invention relates to augmented reality, and more particularly towards a device for augmenting a view with information.
2. Discussion of the Prior Art
Virtual reality is used in many diverse fields, such as kitchen design and military training. Virtual reality emerses a user in a digital environment, where the user's perceptions of sight and sound are manipulated by a computer. While virtual reality provides inexpensive alternatives to building a mock-up of a kitchen or firing live ammunition during an exercise on a battlefield, virtual reality systems lack the sophistication of human perception.
Virtual reality systems have evolved into augmented reality based systems, where a user's perception of a real environment is augmented with information. FIG. 1 is a block diagram illustrating an augmented reality system wherein video images of the environment are combined with computer-generated graphics, according to the prior art. The system includes: a video camera 110; external trackers 112; two dimensional/three dimensional (2D/3D) graphics module 114; an image processing module 116; a pose calculation module 118; a graphics rendering module 120; a video and graphics overlay module 122; and a display 124. As is known, a 3D visual perception may be achieved through use of two cameras and a stereo display.
An augmented reality system can be used to provide guidance to a user, for example, providing information during a surgical procedure. A view of a patient's internal anatomical structures may be overlaid onto a real view of the patient. The internal structures are determined and shown in a graphical representation registered with the view of the real patient.
A head-mounted display (HMD) is a desirable means to display an augmented view to a user. Various HMDs are depicted at http://www.cs.unc.edu/˜us/web/headmounts.htm. A HMD allows the user to vary the viewpoint by turning his or her head. However, HMDs are typically cumbersome, especially over longer periods. The weight of a HMD may put a significant strain on a user's neck and back, especially if the user assumes a pose with a tilted head.
The prior art teaches that the difference between the user's natural eye-point and the viewpoint of the video camera is a concern. The prior art proposes designs which attempt to align an imaging camera with the user's line of sight. Designs have been proposed to further include beam combiners to align the optical axis of a camera and a user, e.g., A. Takagai, S. Yamazaki, Y. Saito, and N. Taniguchi, “Development of a Stereo Video-See-Though HMD for AR Systems,” IEEE and ACM Int. Symp. On Augmented Reality—ISAR 2000 (Munich, Germany, Oct. 5-6, 2000), pages 68-77. However, these systems do not address the comfort associated with wearing a HMD, particularly when the user assumes a pose with a tilted head.
For registration between the view of the real environment and the augmenting graphics, the user's viewpoint needs to be tracked. In prior art, head-mounted tracking cameras have been used for optical-see-through displays (where the user sees the real environment through a semitransparent display that shows additional graphics), but not for video-see-through displays. An example of an optical-see-through HMD with two head-mounted tracking cameras in conjunction with a magnetic tracker is described by Thomas Auer and Axel Pinz in “Building a Hybrid Tracking System: Integration of Optical and Magnetic Tracking”, Proceedings of the 2nd IWAR'99, IEEE Computer Society, (IWAR'99, San Francisco, Oct. 20-21, 1999. In the case of video-see-through HMDs, a method has been proposed which uses the views captured by the imaging cameras for tracking, and a magnetic tracker. See State, Andrei, Gentaro Hirota, David T. Chen, William F. Garrett, and Mark A. Livingston. “Superior Augmented-Reality Registration by Integrating Landmark Tracking and Magnetic Tracking.” Proceedings of SIGGRAPH 96 (New Orleans, La., Aug. 4-9, 1996); Computer Graphics Proceedings, Annual Conference Series 1996, ACM SIGGRAPH, pgs. 429-438. However, the tracking capabilities exhibited by the known prior art systems are not suitable in a practical setting for tasks needing precise graphical registration.
Therefore, the need exists for a system and method including a dedicated tracking camera and a downward pitched imaging camera.